1. Field of the Invention
The present invention relates to a digitizer for raster digitizing an image. An image here is a generic reference to an image, map, drawing, microfiche, microfilm or any other paper or film product. The digitizer can also capture either black and white or color media. The image will be mounted on a stage which is movable by linear motors and can be "patch" illuminated by using fiber optic bundles. The digitizer can capture data over a wide range of resolutions and includes an adaptive dynamic range feature.
2. Description of the Background Art
Various digitizers are known in the art. However, these digitizers are not suitable for use in nonstationary environments such as on a ship, land vehicle, aircraft or spacecraft. Therefore, use of these digitizers is limited.
Moreover, many conventional digitizers are rather large and are very sensitive. Therefore, these digitizers are susceptible to vibration and they create scan artifacts when digitizing an image.
Additionally, many conventional digitizers are not satisfactory when scanning a large image. Either the digitizers are not equipped to move the digitizing camera or stage holding the image over a large area or the digitizers will store an unnecessary amount of data concerning the entire image. Feature scanning cannot be accomplished by some conventional digitizers. Memory requirements for these conventional digitizers therefore increase and the speed at which an image can be digitized decreases.
Conventional digitizers also use gear or screw arrangements for moving the camera or stage upon which the image is mounted. Therefore, there is an initial friction between the gears which must be overcome before positioning of the stage can be carried out. This initial friction slows down the scanning process and reduces accuracy in the positioning of the image. Additionally, lead screws are difficult to extend to large sizes for accommodating larger media types. Longer lead screws tend to bend easily resulting in problems in both accuracy and reliability.
Conventional digitizers that utilize a two-dimensional array do not provide the capabilities to achieve truly seamless mosaics--namely, deskewing and keystoning adjustments. It is not possible mechanically to achieve perfect alignment between the axis of travel and the sensor axis. This misalignment must be computed and accounted for by deskewing the acquired image. Furthermore, mechanical limitations prevent light rays passing through the focal plane of the camera from being perfectly orthogonal to the film platen--resulting in trapezoidal-shaped pixels (referred to as keystoning in the art). When trapezoidal images are mosaiced in contiguous patches, the resultant image contains gaps and overlaps. Conventional digitizers do not account for keystoning, thereby limiting their ability to achieve truly seamless mosaics.
When digitizing an image, conventional digitizers are not concerned with providing uniform illumination to the image. Therefore, deviations in scanning the image can occur and the sensitivity of the camera is decreased. Additionally, variations in the amount of lighting cannot be accommodated nor can differences between each pixel of the digitizer be easily accommodated. Also, many conventional digitizers are unacceptable for digitizing X-rays and other images having dark regions. A better gray scale resolution in the digitizing art is therefore needed.
Accordingly, a need in the art exists for additional forms of digitizers which are suitable for use in nonstationary environments and which overcome the above-noted drawbacks of conventional digitizers.